Polymerase chain reaction amplification of a portion of the genome of both rapidly growing mycobacteria and nocardia, followed by restriction fragment length polymorphism analysis of the amplification products, is being evaluated to assess the utility of these procedures for use in the diagnostic laboratory. The technique has already proven useful in providing preliminary identification of these organisms within a few days of organ-ism isolation, as compared with the month or more required for conventional identification based on biochemical testing. In addition, these molecular procedures seem generally to allow more accurate discrimination among species and subspecies than is possible with biochemical testing. Our work with a portion of the genome for 16S ribosomal RNA has suggested the existence of a hitherto unrecognized Nocardia species. A manuscript describing our methodology and summarizing our findings to date will be submitted for publication. Further studies will be performed on the organisms which may represent new species in the genus Nocardia.